Buggy code:
public class RBTree { static Consumer < RBTree . RBNode > dummyConsumer = ( a ) -> { } ; private enum Color { Black , Red ; } private enum Direction { Left , Right ; } private RBTree . RBNode rootDummy ; private int size ; private RBTree . RBNode minNode ; private RBTree . RBNode maxNode ; private RBTree . RBNode nil ; public RBTree ( ) { } public RBTree ( Iterable < Map . Entry < Integer , String > > items ) { } public RBTree ( Map < Integer , String > map ) { } public void insertItems ( Map < Integer , String > map ) { } public void insertItems ( Iterable < Map . Entry < Integer , String > > items ) { } public void toMap ( Map < Integer , String > map ) { } public TreeMap < Integer , String > toTreeMap ( ) { } public boolean empty ( ) { } public String search ( int k ) { } private RBTree . RBNode searchNode ( int k ) { } private RBTree . RBNode getPositionByKey ( int k ) { } private int insertFixup ( RBTree . RBNode toFix ) { int colorSwitchCount = 0 ; while ( ( ( ( toFix != ( nil ) ) && ( toFix != ( root ( ) ) ) ) && ( toFix != ( rootDummy ) ) ) && ( ( toFix . parent . color ) == ( RBTree . Color . Red ) ) ) { <START_BUG> RBTree . Direction direction = toFix . relationToParent ( ) ; <END_BUG> RBTree . Direction opposite = oppositeDirection ( direction ) ; RBTree . RBNode uncle = toFix . parent . parent . getChild ( opposite ) ; if ( ( uncle . color ) == ( RBTree . Color . Red ) ) { toFix . parent . color = RBTree . Color . Black ; uncle . color = RBTree . Color . Black ; toFix . parent . parent . color = RBTree . Color . Red ; colorSwitchCount += 3 ; toFix = toFix . parent . parent ; } else { if ( ( toFix . relationToParent ( ) ) == opposite ) { toFix = toFix . parent ; toFix . rotate ( direction ) ; } toFix . parent . color = RBTree . Color . Black ; toFix . parent . parent . color = RBTree . Color . Red ; colorSwitchCount += 2 ; toFix . parent . parent . rotate ( opposite ) ; } } root ( ) . color = RBTree . Color . Black ; colorSwitchCount += 1 ; return colorSwitchCount ; } public int insert ( int k , String v ) { } public int delete ( int k ) { } private int deleteNode ( RBTree . RBNode node ) { } private int deleteFixup ( RBTree . RBNode x ) { } private RBTree . RBNode successor ( RBTree . RBNode node ) { } private RBTree . RBNode predecessor ( RBTree . RBNode node ) { } private RBTree . RBNode subtreeMin ( RBTree . RBNode node ) { } private RBTree . RBNode subtreeMax ( RBTree . RBNode node ) { } private RBTree . RBNode root ( ) { } public String min ( ) { } public String max ( ) { } int minKey ( ) { } int maxKey ( ) { } private class IndexedConsumer < T > implements Consumer < T > { int index ; BiConsumer < T , Integer > base ; public IndexedConsumer ( BiConsumer < T , Integer > baseFunction ) { } public void accept ( T arg ) { } } private void walkPreOrder ( RBTree . RBNode node , Consumer < RBTree . RBNode > consumer ) { } private void walkInOrder ( RBTree . RBNode node , Consumer < RBTree . RBNode > consumer ) { } private void walkPostOrder ( RBTree . RBNode node , Consumer < RBTree . RBNode > consumer ) { } private void walk ( RBTree . RBNode node , Consumer < RBTree . RBNode > consumerPre , Consumer < RBTree . RBNode > consumerIn , Consumer < RBTree . RBNode > consumerPost ) { } public int [ ] keysToArray ( ) { } public String [ ] valuesToArray ( ) { } public int size ( ) { } RBTree . RBNode select ( int index ) { } int selectKey ( int index ) { } void printTree ( ) { } void printTree ( PrintStream stream ) { } void checkTreeInvariants ( ) { } private void checkTreeInvariants_ ( ) { } private int checkSubtreeInvariants ( RBTree . RBNode node ) { } private RBTree . Direction oppositeDirection ( RBTree . Direction direction ) { } private class RBNode { public RBTree . RBNode parent ; public RBTree . RBNode left ; public RBTree . RBNode right ; public RBTree . Color color ; public int key ; public String item ; public RBNode ( RBTree . RBNode parent , RBTree . RBNode left , RBTree . RBNode right , RBTree . Color color , int key , String item ) { } public RBNode ( RBTree . Color color ) { } public RBTree . RBNode getChild ( RBTree . Direction direction ) { } public void setChild ( RBTree . Direction direction , RBTree . RBNode node ) { } public void rotate ( RBTree . Direction direction ) { } public void setLeft ( RBTree . RBNode node ) { } public void setRight ( RBTree . RBNode node ) { } public void transplant ( RBTree . RBNode node ) { } public void replace ( RBTree . RBNode node ) { } public void rotateLeft ( ) { } public void rotateRight ( ) { }

Fix:
RBTree . Direction direction = toFix . parent . relationToParent ( ) ;